Lecture Data communications and networks: Chapter 15 - Forouzan

LANs do not normally operate in isolation. They are connected to one another or to the Internet. To connect LANs, or segments ofLANs, we use connecting devices. Connecting devices can operate in different layers of the Internet model. In this chapter, we discuss only those that operate in the physical and data link layers.

Chapter 15 Connecting LANs, Backbone Networks, and Virtual LANs 15.1 Copyright © The McGraw­Hill Companies, Inc. Permission required for reproduction or display 15-1 CONNECTING DEVICES In  this  section,  we  divide  connecting  devices  into  five  different  categories  based  on  the  layer  in  which  they  operate in a network Topics discussed in this section: Passive Hubs Active Hubs Bridges Two­Layer Switches Routers Three­Layer Switches Gateways 15.2 Figure 15.1  Five categories of connecting devices 15.3 Figure 15.2  A repeater connecting two segments of a LAN 15.4 Note A repeater connects segments of a LAN 15.5 Note A repeater forwards every frame; it has no filtering capability 15.6 Note A repeater is a regenerator, not an amplifier 15.7 Figure 15.3  Function of a repeater 15.8 Figure 15.4  A hierarchy of hubs 15.9 Note A bridge has a table used in filtering decisions 15.10 Figure 15.9  Finding the shortest paths and the spanning                            tree in a system of bridges 15.16 Figure 15.10  Forwarding and blocking ports after using spanning                              tree algorithm 15.17 Figure 15.11  Routers connecting independent LANs and WANs 15.18 15-2 BACKBONE NETWORKS A  backbone  network  allows  several  LANs  to  be  connected.  In  a  backbone  network,  no  station  is  directly  connected  to  the  backbone;  the  stations  are  part of a LAN, and the backbone connects the LANs.  Topics discussed in this section: Bus Backbone Star Backbone Connecting Remote LANs 15.19 Note In a bus backbone, the topology of the backbone is a bus 15.20 Figure 15.12  Bus backbone 15.21 Note In a star backbone, the topology of the backbone is a star; the backbone is just one switch 15.22 Figure 15.13  Star backbone 15.23 Figure 15.14  Connecting remote LANs with bridges 15.24 Note A point-to-point link acts as a LAN in a remote backbone connected by remote bridges 15.25 15-3 VIRTUAL LANs We  can  roughly  define  a  virtual  local  area  network  (VLAN)  as  a  local  area  network  configured  by  software, not by physical wiring Topics discussed in this section: Membership Configuration Communication between Switches IEEE Standard Advantages 15.26 Figure 15.15  A switch connecting three LANs 15.27 Figure 15.16  A switch using VLAN software 15.28 Figure 15.17  Two switches in a backbone using VLAN software 15.29 Note VLANs create broadcast domains 15.30 ...                           tree in a system of bridges 15. 16 Figure? ?15. 10  Forwarding? ?and? ?blocking ports after using spanning                              tree algorithm 15. 17 Figure? ?15. 11  Routers connecting independent LANs? ?and? ?WANs 15. 18 1 5- 2... IEEE Standard Advantages 15. 26 Figure? ?15. 15  A switch connecting three LANs 15. 27 Figure? ?15. 16  A switch using VLAN software 15. 28 Figure? ?15. 17  Two switches in a backbone using VLAN software 15. 29... Figure? ?15. 6  A learning bridge? ?and? ?the process of learning 15. 13 Figure? ?15. 7  Loop problem in a learning bridge 15. 14 Figure? ?15. 8  A system of connected LANs? ?and? ?its graph representation 15. 15 Figure? ?15. 9  Finding the shortest paths? ?and? ?the spanning